The present invention relates to apparatus for deriving valid background absorption compensation in a spectrophotometer when the intensity of the continuous spectrum emitting radiation source therein varies beyond optimum levels. It is commonly known in the art that readouts of spectrophotometers can be compensated for background absorption if radiant energy sources for emitting a resonance line of the sample being evaluated and a continuous spectrum containing the resonance line are included therein. Of course, the prior art for such compensation is predicated on the assumption that the background absorption of the continuous spectrum emitting radiation source is the same for all wavelengths in the spectrum thereof and at any intensity of that source. However, this assumption is not strictly valid and as the intensity of the continuous spectrum emitting radiation source varies over wider ranges, the background absorption compensation derived therewith becomes less accurate.